In wireless communications, users situated relatively far from a base station that serves them are generally more susceptible to interference from neighboring base stations and to signal attenuation. As a consequence, such users may experience relatively low signal-to-interference-and-noise ratios (SINRs), and thus typically receive much lower data rates than users located nearer to the base station. The relatively distant users are referred to as “cell edge users” or as users with “poor geometry.” It will be understood that when one user is said to be more “distant” from the base station than another, what is meant does not depend solely on geographical distance, but also to susceptibility to other factors leading to attenuation and interference. It is noted that the terms “user” and “mobile station” are generally used interchangeably herein to denote a mobile entity or device operative to exchange communications signals with the wireless communication system. Any deviation from such interchangeability should be apparent from the context.
Wireless packet data systems of the current art (for example, systems implemented according to the Evolution-Data Optimized (EV-DO), High Speed Packet Access (HSPA), or Worldwide Interoperability for Microwave Access (WiMAX) wireless protocols)), as well as those projected for deployment in the near future, such as the 3GPP Long Term Evolution (LTE) project), use schedulers located at base stations to determine transmission timing and format—including data rate, modulation and coding rates, power and frequency allocation—for data transmissions to the mobile users. Based on channel quality feedback from the mobile stations, the schedulers attempt to transmit to users in a manner to take advantage of favorable quality conditions in these channels. Further these schedulers implement scheduling algorithms for balancing the competing demands of all the users seeking to receive data from each base station, using fairness criteria that take into account the throughputs and latencies experienced by the users.
A significant performance issue, however, associated with wireless packet data systems is the great disparity between the data rates that are achievable for users near the base station sites and those users that are further away at the cell edge.
To some degree, the poorer channel quality typically experienced by mobile users at the cell edge is mitigated by increasing transmit power and bandwidth at the base station and by the addition of multiple antennas at the base station to support multiple data stream transmission and/or beam-forming to the mobile station. Nonetheless, even with such signal quality enhancements, those mobile stations at the cell edge are still limited to low data rates and cannot realize the quality of service required for newer, low-latency, high data-rate wireless applications. Moreover, even to the degree the mitigation steps described here improve throughput for cell-edge users, they also tend to further improve throughput for users better positioned in the cell, so that the problem of disparity in throughput between cell-edge and other users remains largely unaddressed.